Thursday, August 9, 2018

2018 ~ The Year of SSB Transceivers

Something for the SDR Crowd!

You too can build your own SDR Transceiver!Second Generation Main Board

The board above is a second generation board and contains the two ADE-1 Detectors and the Modem coupling transformers, the divide by four 74AC74 and to be installed is the band pass filter. If you look close you can see the ferrite core balun used to split the signals going into the two detectors. This is a deliberate attempt at isolating signals and keeping things neat and tidy. I am thinking about a separate enclosure just for this board. Later today I will install the bandpass filter with the intent that it may be used at 9 MHz with a possibility of a different front end. You will have to stay tuned for this.

How about using the SDR on WSPR?

While I can claim I built this rig and added several modifications, by and large the credit goes to Charlie Morris ZL2CTM for his design and software development. You can follow ZL2CTM on YouTube and he has many videos and tutorials!

The bottom line is how your signal sounds AND LOOKS at the other end. I am really surprised at the number of hams that use either an SDR rig in the shack or use an SDR receiver on the Web for the receiving end of things. Not too many are using a homebrew SDR! Thus it is not unusual to hear that my signal looks really good. To date I have made close to three dozen contacts including a 8000 mile DX QSO with a station in Australia --on 40 Meters. My usual set up is the rig followed by a 100+ watt Solid State Amp kit from CCI and then the Heathkit SB200. Based on my upgrade of the SB200 I typically see in excess of 600 Watts to the antenna. That is a smoking signal!

My 40M antenna is a droopy dipole and that means if I spent a bit more time on the antenna I would hear and work more stations. The center pole is up about 25 feet and the length is 98 feet 3/2 wavelengths on 20 Meters. It is in the shape of an L as it runs along the back end and one of the sides of the lot. The fiberglass support pole is strapped to the tree.

But let us start with the Block Diagram of the basic hardware. Beyond this I have a transmit Driver Stage with a 2N3904 and 2N3866 and the Final amplifier is a IRF510. The relay Switched J310's and the audio amplifier (2N3904 + LM386) are located on the main receiver board. One other item needed to make this play is another bit of hardware from PJRC and that is the sound isolator which I think is nothing more than a modem transformer sealed in a box. The Codec board needs to keep the DC and AC grounds isolated and this is what this device does. In line you hear the amazing SDR signals -- out of the circuit and straight through coupling --garbage!!!!!! It cost $6. One of my modifications was to add modem coupling transformers following the ADE-1's --again the same issue as with the sound isolator. You simply cannot ugly construct this rig and have expectations for success! You will note the date on the block diagram and you will realize this has been a year in the works.

(R1 is for Simulation Purposes in LT Spice and not used in the final circuit)

The above circuit forms the basis of the driver stage and has been used on many transceiver projects. Ignore the notes and focus on just the 2N3904 and 2N3866 parts of the circuit.

This circuit is used for the Final RF amplifier stage on the SDR. Now a modification to this circuit to accept the Mitsubishi RDHF RF FET would include the replacing the Zener with the 78L05 three terminal regulator and inserting a LED in between the Ground pin of the 78L05 and Ground. which raises the output voltage > 6 VDC. A higher bias level is needed for the RF FET. Typical output is 6 Watts but higher levels close to 10 watts may be experienced. All other circuit constants remain the same. this is an easy conversion. What is so cool about the LED -- when the circuit is biased "ON" the LED glows --more lights, bells and whistles.

Below are a couple of additional schematic circuits for the SDR Rig with the first being the steerable Dual J310 Amp stage. R3 is for simulation purposes and not used in the final build. R7 is as noted is a 10K trimpot connected as a variable resistor. Note the schematic shows the amp stage amplifying from left to right but the actual install has the amp stage direction going from right to left. I just know someone will install it backwards and then email that it doesn't work. RTM!

The Below sketch shows the modem transformer install.

Now you ask why would you do this when you can buy the IRF510 for about 80 cents and the RDHF is about $5. Well it all depends if you want to operate above 20 Meters. The power output drops off at higher frequencies with the IRF510. So it is all about choice of operating frequency.Why even the microphone was homebrewed (a first for me). I bought this electret Lavalier style microphone from All Electronics. It is a superb microphone but somewhat costly -- about $1.15 with 15 foot cord. It does not have a PTT switch so I built the PTT using a microswitch I had in the junk box. Starting with a piece of scrap 2X4 about 6 inches long I milled out a cavity so I could mount the microphone and PTT. The remainder of the 2X4 was simply sawed off and ths is what was left. It is palm sized. See below. Aside from some splinters all went well. Not bad for some junk parts a piece of scrap wood and a $1.15 microphone. If you look closely you can see the PTT button sticking out of the case. Not very elegant but it works.

As of 8/11 I have had about 3 dozen contacts including one this morning with a VK station on 40M.My homebrew Electret Microphone: (This is one heck of a buy!)

Started like This...

This rig was built based on the design/software from Charlie Morris, ZL2CTM. This is a truly amazing rig as no external computer is required to make it play. While something more than an Arduino Uno R3 is required to make it work, the Teensy 3.5 and the Audio Codec Board from PJRC will make it stand up tall. This is a $150 class rig but offers many possibilities for use on multiple bands or as I have on the drawing boards a hybrid Crystal Filter/SDR rig.

8 comments:

I really love watching Charlie's YouTube videos on his projects. He goes into great detail on the design of his projects. In many he does a great job of explaining the math used in selecting component values for the circuits. Along with the SDR he is now in the process of designing and building a Hardware Defined 80 and 40 meter SSB CW trahsceiver. You can check all of his videos at https://www.youtube.com/channel/UCSNPW3_gzuMJcX_ErBZTv2g/featured?disable_polymer=1DuWayne

Hi DuWayne, Thanks for the post. yes Charlie does a superb job and his videos as you say are detailed and very explanatory. His new transceiver will indeed cause many irons to be lit off. 73's Pete N6QW